The present invention relates generally to motion picture projectors and more particularly to a projector that is provided with a high intensity projection arrangement and a power supply unit interconnected to the projector to supply all the voltage and power requirements of the projector. The power supply unit and the projector are further provided with a control arrangement to prevent shock hazards and a selection arrangement to facilitate the supply of a standard predetermined voltage to the projector for various conventional supply inputs to the power supply unit.
It is advantageous to provide projection apparatus that is utilized in educational, institutional and entertainment applications with a high intensity light source. In addition to the obvious advantages of clearer and more distinct images at predetermined distances and surrounding light conditions, the high intensity light sources have a significantly longer operating life, as much as 20 times that of conventional lamps, and therefore lower maintenance requirements. Further, it would be desirable to modify existing projectors by replacing the conventional projection lamp by a high intensity lamp with as few modifications and additions to the projector as possible.
The high intensity lamps available for this purpose contain an inert gas, such as xenon, which is under pressure and which is ionized to produce and sustain an arc across a small gap approximately 100 thousandths of an inch which is formed between two electrodes. The power requirements to operate the high intensity projection lamp are a short duration starting pulse of approximately 25,000 volts in magnitude to initiate the arc and a DC supply with capabilities in the range of 15 to 20 volts at approximately 20 amps to sustain the arc.
In order to facilitate the modification of conventional projectors as well as to maintain the size and weight of the projector within reasonable limits for average operating circumstances, it is desirable to provide the circuitry supplying the power requirement of the high intensity projection lamp in an enclosure separate from the projector housing. Thus, the projector and the power supply unit are interconnected by a cable supplying the 25,000 volt starting pulse and the DC sustaining voltage. To further minimize the modifications to conventional projectors and to increase the adaptability of the high intensity projector apparatus, it is also desirable to operate the apparatus from various conventional input supply sources as found in military and international applications.
However, while the above-described arrangement is generally suitable for operation of high intensity projection apparatus, substantial shock hazards exist and undesirable operating conditions may occur.